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Put The Bite On Bugs

Monday, April 1, 2002
filed under: Insects

Sunflower Growers Urged to Step Up Insect Management

Monitor insect development closely, time treatments if they’re needed,

and you’ll be able to control several insects at the same time.

Sunflower growers should monitor insect development closely and time treatments, if they’re needed, to control several insects at the same time, including the Lygus bug, an insect threat that has raised concerns with confection processors in the Northern Plains.

Confection processors have been noticing an increase in small, brown spots on the meats of confection sunflower, resulting in kernels that are unattractive to buyers, and distasteful to consumers. Oil sunflower hulled and used for confectionery purposes are equally susceptible to brown spot.

The Lygus bug (also called tarnished plant bug) is believed to be the cause of brown spot in sunflower kernels. The insect feeds on flowering broadleaf crops such as alfalfa and canola, then moves to late-season crops such as sugarbeets and sunflower. The Lygus bug isn’t really a new insect in the area, it’s just that its populations are higher than before, possibly due to more broadleaf crops grown in the region, according to North Dakota State University entomologist Gary Brewer.

Crop scientists suspect that in the process of feeding on developing sunflower kernels, the adult Lygus bug injects digestive enzymes, and then extract nutrients with its needle-like mouthparts. Evidence of feeding activity is microscopic and can’t be seen with the naked eye, but the damage becomes apparent later as brown spots on hulled sunflower kernels. (For more background on the Lygus, see article in the January 2001 issue of The Sunflower, which can be found online at the National Sunflower Association’s web site, Click on “The Sunflower Magazine,” then “The Archives”).

Crop scientists at the USDA-ARS Northern Crop Science Lab in Fargo, ND have been studying the problem. This winter, they conducted a greenhouse experiment in which adult Lygus bugs were released on bagged confection sunflower heads at prebloom (R-4). “We came up with a bunch of seed damage. We had a control head that did not have any damage. So that tells us the Lygus are doing damage,” says Theresa Gross, research technician. Each sunflower head in the study was bagged with five Lygus bugs, and on one sunflower head, 115 Lygus bugs were counted after the study was over. “That indicates they can multiply and survive quite well on sunflower,” says Gross.

A significant number of sterile seeds were the result of another greenhouse experiment in which 10 Lygus bugs were placed on confection sunflower heads. Some researchers have implicated a type of fungus called Alternaria, which may cause similar brown spot symptoms on sunflower kernels. Spray trials conducted in ND by Tom Gulya, USDA-ARS plant pathologist and USDA-ARS entomologist Larry Charlet, both of Fargo, appear to rule out the involvement of Alternaria, but another test is under way to offer further proof of that.

Additional field research on the Lygus is planned this summer, in which Charlet hopes to involve other crops. “It could be that Lygus populations and damage in sunflower are worse if its next to canola or beans, we just don’t know at this point,” he says. The impact of cropping systems, the growth stage in which sunflower is most susceptible, the economic threshold for confection sunflower damage, and treatment timing are key questions in need of answers, says Charlet.

Treat to Control Several Insects

Entomologists suspect sunflower is susceptible to Lygus bug damage during flowering, from anthesis through seed hardening. According to data from other parts of the country. Organophosphate (Lorsban, Methyl Parathion, Parathion) and pyrethroid (Asana XL, Baythroid, Scout X-Tra, Warrior) insecticides have shown success in controlling the Lygus bug. Although none of these products is currently labeled for control of Lygus on sunflower, Lygus bugs can be treated at the same time sunflower is treated for other insects, such as the seed weevil and banded sunflower moth.

In some cases, entomologists believe that two treatments are needed to protect confection sunflower from seed feeding insects: One application at the onset of pollen spread or approximately 10% bloom, then a second treatment seven days later. This regimen should adequately control insects on confection sunflower throughout flowering.

Can growers get by with one treatment? Entomologists, empathetic to market prices and crop production costs, advise producers to watch their developing sunflower crops and use their best judgement. If Lygus bugs, banded sunflower moth, or the red seed weevil are present, treat sunflower at 10% bloom (R-5) for sure. It’s possible that one treatment—or one treatment along with a second treatment around the perimeter of a sunflower field—will be sufficient. However, applying only one treatment may risk damage if one or more insects re-infest the crop again while it’s still vulnerable to damage.

“We don’t really know if one application will be enough (to control Lygus). We’re quite certain that the insect will be susceptible to treatment, but it is very mobile, and it may move in again after a first treatment,” says Brewer.

Confection sunflower producers in particular should consider two treatments, says Phil Glogoza, NDSU extension entomologist. “If you’re trying to minimize injury from the seed weevil, the banded moth and now the Lygus, you have about 10 days minimum where you need good protection, and with the insecticides we use now, one application is not going to do that,” says Glogoza. “With the banded moth generally infesting earlier than the seed weevil, that’s why we suggest an application at early flowering, when there’s about a 10% pollen ring and about 25% of the plant is showing ray petals, and then a second application five to seven days later. That should provide close to two weeks of control, which should be adequate to protect sunflower from these three major pests.”

Other Bugs, Other Areas

Of course, there are insects to watch besides the Lygus. The banded sunflower moth is one insect that perhaps should receive more attention. “I think we’ve been slipping and taking more losses than we need to with that one,” says Brewer. Still, no one insect stands out as a regional threat. Rather, there are localized “hot spots.” Although the red seed weevil has increased in population in some areas, it still remains a relatively spotty problem, he says. Most growers already know how to look for and manage the sunflower beetle, says Brewer. The sunflower midge has dropped significantly in number from several years ago, and should only be a limited problem.

The sunflower moth (commonly called head moth) historically has been a pest that High Plains sunflower producers need to monitor, says Phillip Sloderbeck, Kansas State University extension entomologist. The stem weevil is another insect that has troubled sunflower in some areas of the High Plains, especially in areas with significant sunflower acreage. Sloderbeck says the Lygus bug generally has not been a problem in the High Plains. However, he has heard more reports of the Dectes (or soybean) stem borer, a type of longhorned beetle, which he says producers and agronomists in the High Plains may want to put on their checklist as an insect to monitor.

Michael Catangui, South Dakota State University extension entomologist, says one county last year in South Dakota also reported the Dectes stem borer in sunflower. One county in the southwest part of the state reported some midge problems, and eight counties in central SD had early-season problems with the pale striped flea beetle in 2000, which is unusual since this insect normally isn’t a crop pest problem in South Dakota. The black stem weevil also caused some stand losses in sunflower last year by feeding on the leaves of sunflower seedlings.

However, South Dakota hasn’t had problems with Lygus. “It looks like we have some insects in South Dakota that are not in North Dakota.” Catangui advises producers in South Dakota to monitor for common sunflower insects, and producers in areas affected by isolated insects such as the pale striped flea beetle and Dectes stem borer should scout for them again this year, since they overwinter.

Processor Perspectives

If anything, the threat of Lygus bugs in the Northern Plains may help refocus attention to insect management. Some Northern Plains confection growers by their own admission say they have been spraying less in recent years, due in part to a lower incidence of red seed weevil. But processors have been noticing an increase in insect damage over the last two seasons, much of it due to banded sunflower moth.

Processors generally discount confection sunflower that doesn’t meet certain quality requirements. Insect damage greater than 2-3% may be subject to price discounts, and higher levels of insect-damaged confection sunflower may even be rejected. On the flip side, some processors may even offer price premiums for confection sunflower deliveries that come in below 2% insect damage. Producers should consult with representatives of the processing company they deal with, since the specifics of each company’s confection contracts are different.

Spray treatments to control insects in confection sunflower are generally recommended by processors, but not stipulated in contracts. “Educating our objectives and concerns to the grower about the benefits of providing cleaner sunflower, and what that means to his finished product, is probably a better way than to dictate how he should grower sunflower,” says Tim Petry, field production manager for Dahlgren and Company Inc, Crookston, MN.

Petry says field representatives will work with growers to manage insect problems, as well as other pest problems such as weeds and disease. He advises confection producers to budget for at least one insecticide application. Petry points out that he knows of some confection producers who sprayed insecticide three times last year. “They knew it was in the best interest of their crop. Contractually, we don’t require spray treatments. We just try to stress that we hope (a contract) is a partnership with us and the grower to put the best possible product that we can in the bin.”

Contract specifications are largely based on what the customer wants, says Dean Pedersen, purchasing manager and agronomist for Agway Inc, Grandin, ND. “I think the industry as a whole has been tightening, based on what the customer wants. And I can understand that side of the equation. I eat sunflower too, and I don’t like the ones that taste bad. Insects and Sclerotinia are two of the top causes of that,” he says. Agway also does not require certain treatments within a contract, says Pedersen. The general guideline is that growers should follow good agronomic and cultural practices when producing confection sunflower, including insecticide treatments if needed, he says.

If a producer does have insect problems in confection sunflower, Petry urges growers to segregate infested sunflowers from crop that was not affected. “If producers can segregate loads with insect hot spots, this would protect the quality of the lot, rather than jeopardize the entire field,” says Petry. – Tracy Sayler

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